Wind energy has long been known to be a clean and safe form of energy. Recently, the use of wind turbines for generating electricity has increased. Most of the generated electricity comes from land-based wind turbines.
However, it is sometimes difficult to find good locations on land for new wind turbines, and it is known that the wind at sea is stronger and more consistent than the wind over land. On the other hand, offshore wind turbines have to be able to withstand considerably harsher conditions and have so far been found to be more difficult and costly to install and to access for maintenance.
Therefore, much effort has been spent on developing wind turbines suitable for offshore use.
Since the establishment of reliable and cost-efficient wind turbine foundations in offshore locations in particular has been found to be a major challenge, one approach has been to develop floating wind turbines for offshore use.
A particularly interesting development is floating vertical axis wind turbines (VAWTs), in which the floating turbine body of the VAWT rotates in the water, effectively using the water as a kind of bearing.
This approach, which practically obviates the need for the above-mentioned costly and complicated building of wind turbine foundations and provides for a robust and relatively cost-efficient construction, is described in WO 2011/008153 and NL 1035026.
To prevent damage to the wind turbine in, for example, high wind conditions, it is necessary to provide means for controllably reducing the rotational speed of the wind turbine. It would be desirable to provide for such means that are cost-efficient, reliable and safe.